


Alpha Instinct

by thewinchesterlifestyle



Category: Supernatural
Genre: Age Difference, Age Swap, Alpha Sam, Fingering, Incest, Knotting, M/M, Mating Cycles/In Heat, Morally Ambiguous Character, Older Sam, Older Sibling Sam, Omega Dean, Rough Sex, Sibling Incest, Size Difference, Size Kink, Teen Dean, Top Sam, Virgin Dean, Younger Sibling Dean, dubcon, naive dean, very dubcon
Language: English
Status: Completed
Published: 2016-12-05
Updated: 2016-12-05
Packaged: 2018-09-06 18:55:39
Rating: Not Rated
Warnings: Underage
Chapters: 1
Words: 1,393
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8765059
Author URL: https://archiveofourown.org/users/thewinchesterlifestyle/pseuds/thewinchesterlifestyle
Summary: Sam wakes up to the sound and scent of Dean, newly presented Omega, going into Heat.





	

**Author's Note:**

> Written for a prompt where the roles of older/younger brother are swapped and the age gap between Sam/Dean is several years more.

Sam groaned and rutted against the cheap mattress under him. The syrupy sweet scent of an Omega in Heat saturated his senses and had him reaching down to touch his aching cock. Lazily he stroked himself and groaned into the pillow. It took him a few moments of jerking himself off to notice the other sounds in the room.

 _Whimpering_.

Slowly he lifted his head and glanced over to see Dean twisting on his bed. The whimpers got louder and the smell of fertile Omega increased in the heavy air.

“ _Fuck_.” Sam’s cock was aching and the Alpha in him was  _demanding_  that he pin the fertile bitch down, shove his cock in and fuck until his knot had caught. He squeezed his eyes shut and knew his eyes were burning red.

It was thirty minutes of listening to Dean whining and whimpering on his bed, of breathing in one of the most enticing scents he’d ever smelled that had the predator in him fixating and growling lowly at the distance. But after thirty minutes of being completely aware of what exactly was in the bed next to him it was impossible not to act.

A _newly presented Omega_ was too much for him to resist for long no matter how wrong it was to take advantage of such a young Omega.

Sam threw back his covers and closed the short distance between their beds. It took a little to untangle Dean’s legs and to strip off his shirt before turning to the boxers that were stuck to Dean’s ass with slick. Once he’d successfully removed Dean’s soaking wet boxers and thrown them aside heatscent was even thicker in the air.

He stood there breathing in and savoring the delicious smell. “Burnin’.” Dean’s voice was rough as he came awake slowly. “Sammy I’m burnin’. Why does it hurt?”

Omega gold eyes were blinking at him with something dazed and very confused in them. “I’m going to take care of that.” Sam was quick in stripping himself and pressing Dean into the proper position.

“Please Sammy make it stop.” Sam _knew_ Dean didn’t know what he was asking, that this far into his Heat he wasn’t aware of much of anything but Sam couldn’t and wouldn’t think beyond putting his cock in a wet cunt.

He stroked a hand down Dean’s back and rubbed at the nape of the young Omega’s neck until Dean had relaxed.

Being this close to an in-Heat Omega tested every last bit of his will power. He barely restrained himself enough to sink fingers into Dean’s wet heat, stretching his little brother open instead of immediately pushing his cock inside like his instincts wanted him to.

Dean’s little cunt was soaked.

The entire time Dean was whimpering and shoving his ass back into him, too far gone to care much for anything but his instinct to seek a knot and Sam was the closest Alpha.

“You’re so loose already.” Sam knew his voice was rough sounding as he twisted his fingers inside Dean and pressed against his little brother’s prostate until Dean was practically howling.

Slick was practically gushing out of Dean, making a mess of his sheets and coating his thighs.

It was good enough. Even a virgin Omega’s cunt would naturally loosen during a Heat to encourage quicker breeding and easier access for nearby Alphas.

Sam stroked his fingers up and down his long, thick Alpha cock a few times. He regretted the low light in the room because he was missing what was sure to be a gorgeous sight of Dean’s first Heat. “Going to fuck your cunt full, little brother. Don’t worry I’ll take very good care of you.”

The first two inches inside Dean was Heaven. He could feel Dean’s inner walls clenching and unclenching around him, trying to drag him in deeper and lock down on him.

There was a low whine when he pushed further in and Dean’s body was tense but he took every single inch of Sam’s cock as his cunt yielded beautifully for the Alpha cock sinking inside him. “Oh.” Dean gasped it and his whole body shuddered when Sam started snapping his hips forward. “It’s huge… _Alpha_.”

Sam  _knew_  how impressive his cock was. He was long and thick. It was something the Omegas he’d fucked in the past had loved and now he was about to fuck Dean. He should have known Dean wouldn’t be anything other than an Omega when he’d caught sight of Dean’s small cock when his brother had been changing.

At first he’d thought Dean might be a late bloomer but it was obvious the small cock had been the only real evidence he’d needed for Dean’s designation.

He managed several short thrusts, sinking further and further in, as Dean wailed and moaned under him. But every bit of his restraint flew out of the window the second he had Dean wrapped completely around his cock, all hot and warm and wet. Dean’s arousal and need drove him forward until he was slamming inside. The sound of his cock pumping in and out of a soaking wet Omega cunt along with his balls slapping against Dean’s ass and the sound of their ragged moans mixing in the air sounded filthy to his ears.

“Fuck, you feel so good around my cock, Dean.” Sam curled his hand around the back of Dean’s neck and felt how the _Omega_ under him went completely pliant. Dean was warm and soft, so beautifully responsive. Sam's hand reached around to touch Dean's stomach and he could actually feel his large cock pushing against Dean's belly as he fucked deep. He marveled at how young and small Dean still was but newly presented Omegas always were.

Dean was a perfect Omega. Sam knew their father would find Dean an Alpha, an older one he could trust who would no doubt take advantage of breeding a young, fertile Omega. Sam would at least be secure in knowing that Dean would be far away from hunting when that happened.

It would be better for him in the long run but for now Sam was thoroughly enjoying fucking an eager, virgin Omega. A delightfully young, innocent untouched Omega that had his instincts purring at taking something untouched. This was probably wrong but Omegas were considered 'in season' the second they presented and it would almost be cruel to leave Dean writhing in Heat.

“You’re taking it so well…like a good Omega should.” he started to pound into Dean. Sam moved quicker and shoved himself deep with each thrust.

A snarl escaped him as his knot grew at the base of his cock and started to catch on Dean’s cunt with each stroke. It tugged and popped in and out sending pleasure through him. Sam’s fingers dug into Dean’s hips harshly and he slammed himself inside, circling his hips and moaning when he had finally locked them together.

Under him Dean’s body clamped down on him like a vice and the muscles inside his cunt started to milk Sam for every single drop of his seed. Dean’s hold on him tightened further when he came with a whimper and his body, everywhere except that hungry cunt, went completely slack under Sam.

He lazily ground himself against Dean’s cunt, moaning each time his release teased along his nerves and sent more of his come into Dean’s hot deliciously perfect cunt.

Sam draped himself over Dean’s back and pressed him into the mattress so he could nip at the exposed skin of Dean’s shoulders. His teeth grazed the skin but Sam had enough presence of mind not to claim. Instead he focused on marking Dean’s freckled skin up and grinding forward.

After all Dean couldn’t belong to him that way but it didn’t mean he couldn’t thoroughly enjoy himself throughout Dean’s very first Heat. It would be days and days of fucking a burning, writhing Omega begging him for him and Sam wasn’t strong enough to deny himself something like that.

It would only be a matter of time before their father came back and started looking for an Alpha to give Dean to. He would have to take all the time he could get with Dean before that happened and if that involved him knotted in Dean’s dripping cunt then he’d take it.


End file.
